Liquid silicone rubber compositions that are turned into non-conductive or conductive rubber-like structures when cured by a hydrosilation reaction are known in the art and find wide application in the manufacture of various parts used in electrical, electronic, construction, machine, and other fields. A non-conductive liquid silicone rubber base, which is one of the main components of a non-conductive silicone rubber composition, is prepared by compounding an alkenyl-containing organopolysiloxane with reinforcement silica filler, if necessary, with an addition of a non-conductive inorganic filler. On the other hand, a conductive liquid silicone rubber base, which is one of the main components of a conductive liquid silicone rubber composition, is prepared by compounding an alkenyl-containing organopolysiloxane with a conductive filler, if necessary, with an addition of a non-conductive inorganic filler.
In a majority of cases, these starting materials are produced in a batch mode by uniformly mixing them in a double arm mixer, Henschel mixer, planetary mixer, etc., or in a continuous process by continuously loading an alkenyl-containing organopolysiloxane and a filler into a double-screw extruder, where the components are mixed with heating and wherefrom the mixture is extruded in a continuous flow (see Japanese Patent Publication H4-280082). Japanese Unexamined Patent Application Publication [hereinafter “Kokai”] H10-152563 discloses a method for preparation of a liquid silicone rubber base by mixing and distributing a finely powdered conductive filler, such as a carbon black, with a liquid alkenyl-containing organopolysiloxane in a continuous mixing apparatus having a rotary disk that rotates with high speed. Since preparation of such a liquid silicone rubber base occurs at a high temperature caused by procedural heating or friction heating, the obtained liquid silicone rubber base cannot be used directly after the preparation since, prior to curing, it should be cooled to room temperature and then compounded with a cross-linking agent and a curing catalyst. Japanese Patent Publication H07-122000 describes a method for manufacturing a silicone elastomer sponge by curing a mixture of an organopolysiloxane and a curing agent in a silicone rubber base with a foaming agent prepared from an aqueous emulsion that is composed of an emulsification agent, water, and a thickener. However, the cross-linking agent and the curing catalyst have to be added after cooling the silicone rubber base to room temperature, and thus [as in the previously described method] the silicone rubber base cannot be used immediately after the preparation.
On the other hand, a method of manufacturing a silicone rubber sponge from an aqueous emulsion described in Kokai S59-12832 consists of freezing, then thawing and drying a silicone emulsion of a condensation curing type that comprises a hydroxyl end-blocked polydiorganosiloxane, an organic tin catalyst, and a colloidal silica. In addition to an organic amine, thickener, and colloidal silica, the aforementioned emulsion may also be mixed with fillers besides the colloidal silica. However, the process described in the aforementioned publication has a low efficiency as it is time-consuming and requires a large amount of energy to be spent on freezing, thawing, and drying the emulsion.
Kokai 2000-169590 describes a method of manufacturing an elastomer by preparing an aqueous emulsion/dispersion by mixing an aqueous emulsion of a hydrosilation-curable silicone composition with an aqueous dispersion of an adhesion accelerator, silicone resin, and carbon black and applying the obtained emulsion/dispersion onto a fabric substrate as a coating which is then cured. A problem associated with the above method is difficulty of dispersing carbon black in an aqueous medium. Kokai 2002-114860 discloses a method of manufacturing a silicone rubber sponge by heating and curing a mixture composed of a silicone rubber base prepared from an alkenyl-containing polyorganosiloxane and a reinforcement silica filler, a polyorganohydrogen siloxane, a platinum catalyst or an organic peroxide, and a foaming agent composed of a gelatinized water-absorbing polymer that absorbs only water or water with an emulsification agent. However, the gelatinized water-absorbing polymer is extremely viscous and stirring and mixing thereof with other components requires application of very high loads to mixing equipment.